Email sent from forms not received in outlook, but received in webmail

Just found a weird thing:
I've created contact forms on different websites (hosted on different domains) and when i submit the forms sending it the clients addresses, they dont receive the emails. When i send it to my professional email address (on an exchange server) i dont receive it neither. BUT if i send it to my gmail address i receive the notification email...

So it's not a problem of sending the email (which is logged as sent...)

Is there a known issue with the parameters or headers of the email that might have trouble with outlook?

Nope, if the mail is showing up in webmail, it should show up when outlook connects for messages as well.

The one thing I've found over the years is if the site is sending mail to its own domain, but the mail is hosted elsewhere through MX records, sometimes the site doesn't know that it isn't also in charge of mail and just sends it to itself.

So CorpoClient.com has a exchange server, most mail comes from the rest of the web, so it sees the MX record in DNS and sends the message to the mail box. CorpClient.com the website was never configured to know about that MX record, so it sends mail to itself where it never gets read.